The present invention relates to a pierceable stopper used for a liquid container into which a hollow needle can be externally inserted through the pierceable stopper, and also relates to a method of producing the pierceable stopper. More particularly, the present invention relates to a pierceable stopper for a medical liquid bottle or bag filled with a liquid for medical treatment. The pierceable stopper has a pierceable part made of a thermoplastic synthetic resin elastic material and pierceable with a hollow needle for injection or intravenous drip infusion. The present invention also relates to a method of producing the above-described pierceable stopper.
Capsules filled with medical liquids for injection and bottles or bags filled with medical liquids for intravenous drip infusion are preferably designed so that the medical liquids therein can be taken out or a liquid can be injected thereinto without removing the caps or stoppers therefrom. Therefore, the caps and stoppers are arranged so that even when they are pierced with a hollow needle for injection or intravenous drip infusion, the liquids in the containers will not spill out, and, at the same time, foreign matter, e.g. air, in a hospital will not enter the containers. Such stoppers are desirably mass-produced and reduced in cost so as to be used by an increased number of people.
In this case, it is necessary to produce a stopper using a material that will not be torn when pierced with a hollow needle and will not produce even a small gap between the needle and the stopper. At present, vulcanized rubber is used as a material for such a stopper. However, the stopper using vulcanized rubber involves such a danger that an additive, a polymerization solvent, etc. in the vulcanized rubber may flow out into the medical liquid in the container, or rubber chippings may get mixed in the medical liquid. Accordingly, a stopper using a thermoplastic synthetic resin elastic material (hereinafter occasionally referred to as xe2x80x9celastomerxe2x80x9d) has been proposed [see Japanese Patent Application Unexamined Publication (KOKAI) Nos. 61-247460, 61-37242 and 61-131746 (1986)].
There has also been proposed a stopper comprising two layers of the thermoplastic synthetic resin elastomer [see Japanese Patent Application Post-Exam Publication No. 8-2367 (1996)]. However, an experiment carried out by the present applicant reveals that all the proposed stoppers compensate for the disadvantage of vulcanized rubber but are not sufficiently effective in preventing leakage of the medical liquid after the removal of the inserted needle, and none of them are on the practical level.
In view of the above-described problems, an object of the present invention is to provide a pierceable stopper capable of preventing leakage of a liquid from a container after the removal of an inserted needle even if a pierceable part of the pierceable stopper is formed by using a thermoplastic synthetic resin elastic material inferior in elastic recovery force to rubber. Another object of the present invention is to provide a method of producing the above-described pierceable stopper.
Another object of the present invention is to provide a pierceable stopper that can be produced at a reduced cost, and to provide a method of producing the pierceable stopper.
To attain the above-described objects, the present invention provides a pierceable stopper having a pierceable part pierceable with a hollow needle and made of a thermoplastic synthetic resin elastic material, and a stopper body having a higher rigidity than that of the material of the pierceable part. The stopper body has an outer peripheral portion for preventing a stress from propagating to the outside when the pierceable part is pierced with the hollow needle and for defining the pierceable part.
From the viewpoint of minimizing the resistance to penetration of the needle, the lower the hardness of the pierceable part, the better. From the viewpoint of ensuring the mechanical strength as well, however, it is practically desirable to use a thermoplastic synthetic resin elastic material having a hardness in the range of from 20 to 80 in terms of JIS(A) hardness. It is more desirable to use a thermoplastic synthetic resin elastic material having a hardness in the range of from 45 to 65 in terms of JIS(A) hardness.
More specifically, one or more thermoplastic synthetic resin elastic materials are optionally selected from among nylon, polyurethane, olefin, polyester and styrene elastomers having a JIS(A) harness of 20 to 80 degrees and used alone or in the form of a composite or mixed elastomer.
From the viewpoint of elastic recovery force, it is desirable for the pierceable part to be made of at least one selected from styrene and olefin elastomers. From the viewpoint of preventing leakage of liquid, it is preferable that the stopper body be made of a thermoplastic synthetic resin material and thermowelded to the pierceable part.
Regarding the thickness of the pierceable part, a thickness of approximately 1 to 10 millimeters is sufficient to prevent leakage of liquid. However, it is desirable for the pierceable part to have a thickness of approximately 2 millimeters or more with a view to practically eliminating the likelihood of liquid leakage. From the viewpoint of minimizing the resistance to penetration of the needle, a thickness of approximately 8 millimeters or less is preferable. Accordingly, in view of both the liquid leakage and the resistance to penetration, it is desirable for the pierceable part to have a thickness of approximately 2 to 8 millimeters.
The pierceable stopper made of the above-described materials and having the above-described structure is preferably produced by a method as stated below.
According to a pierceable stopper producing method of the present invention, after the stopper body has been injection-molded in an injection mold, a melt of the above-described thermoplastic synthetic resin elastic material is injected into a cavity defined by the injection mold and the stopper body to mold the pierceable part.
According to another pierceable stopper producing method of the present invention, after the pierceable part has been injection-molded in an injection mold, a melt of a thermoplastic synthetic resin material is injected into a cavity defined by the injection mold and the pierceable part to mold the stopper body.
Preferably, the injection pressure of the melt of the thermoplastic synthetic resin material or the thermoplastic synthetic resin elastic material is not lower than 500 kg/cm2. With a view to minimizing the leakage of liquid, an injection pressure not lower than 800 kg/cm2 is even more desirable.
From the viewpoint of minimizing the leakage of liquid, it is preferable that the stopper body be made of a thermoplastic synthetic resin material, and that the stopper body and the pierceable part be thermowelded together in the injection mold by the melt heat of the thermoplastic synthetic resin material or the thermoplastic synthetic resin elastic material.